according to this page
https://cms.paypal.com/uk/cgi-bin/?cmd=_render-content&content_ID=developer/e_howto_api_WPWebsitePaymentsPro
in the Website Payments Pro Regional Differences section, they have a table showing the accepted credit cards for Canada, United States and UK.
accepted cards for the united kingdom are:
Visa, including Visa Electron and Visa Debit
MasterCard
Maestro, including Switch
American Express is only accepted in the US.